Ⅰ、主语从句 (Subject Clause)
　　e.g. That the sea covers about three-fourths of the earth’s surface is well known.
　　e.g. Which design is more practical is still a question.
　　按照英语习惯，有些句子可用it作形式主语，放在句首，而将主语从句放在后面，使句子更为平衡。如上面的句子可改为：
　　e.g. It is well known that the sea covers about three-fourths of the earth’s surface.
　　e.g. It is still a question which design is more practical.
　　小结:
　　主语从句通常位于主语的位置上, 但是有时也可能出现在句子的末尾部分(句子的结构是形式主语的结构). 当句子的主语是从句结构时, 谓语部分应该使用单数的形式.

　　Ⅱ、宾语从句 (Object Clause)
　　宾语从句可以作动词或介词的宾语。
　　e.g. They tell me (that) the math course is difficult.
　　e.g. I wonder whether (if) the refrigerator is large enough.
　　e.g. Please let me know when the telephone will be installed¹.
　　e.g. He informed me of what they wanted.
　　比较:
　　e.g. Please inform him of the fact that I’ve seen her.
　　注：
　　1. 宾语从句通常紧跟在动词和介词的后面。
　　2. 引导宾语从句的连词“that”在口语和非正式文体中常可省略。
　　3. whether和if都可以表示“是否”的意思，在口语中常可以互换，如上面第2个例句，“I wonder”后面既可用“whether”也可以用“if”引出宾语从句，意思不变。但如果作为介词的宾语，或后面跟有“…or not”，或引出主语从句时，则只用whether而不用if，如：
　　e.g. It all depends on whether we can get their cooperation.
　　e.g. Tell me whether you like the handbag or not.
　　e.g. Whether they will join us hasn’t been made clear.
　　他们是否参加我们的活动还不清楚。

　　Ⅲ、表语从句
　　表语从句与系词(以及半系动词)一起构成主句的谓语结构。
　　e.g. My problem is how we can reduce this high temperature.
　　我的问题是我们怎么能够降低这样的高温。
　　e.g. Our conclusion is that, in view of 由于the drought², there is only enough water for two days.
　　for： 就…而言
　　e.g. It is rather cold for January.
　　e.g. She is clever for her age
　　e.g. It seems that it is going to rain. 表语从句
　　It seems that …好像，似乎
　　It seems to me that …我想，我以为
　　e.g. The cloth feels as if it were made of silk. 表语从句

　　Ⅳ、同位语从句
　　同位语从句用以说明名词的内容，使之明确而具体化。跟有同位语从句的名词通常是一些需要进一步说明其具体内容与含义的名词。如conclusion, doubt, fact, fear, hope, idea, news, opinion, suggestion等。从句通常由that引导，有时也可由whether, what, when, where, why, how等引出。
　　e.g.There is no doubt that he will succeed.
　　毫无疑问，他一定成功。
　　e.g.My opinion that no action need be taken yet is shared by most of us here.
　　我的意见是现在还不需要采取行动，这是我们这里大多数人的共识。
　　They haven’t have any idea when it is proper to take action. 对于什么时候适合采取行动, 他们还没有任何想法. /他们还没有想出什么时候适合采取行动
　　提示:
　　在翻译的过程中对同位语从句常常可以采取的处理方式是: “添词”(在同位语从句和从句前的名词之间添加谓语动词)+ “结构转换”(把同位语从句转换成宾语从句的结构)(如: 上面第2个例句); 或者采用“词性转换法+ 结构转换法”(把同位语从句前面的名词转换成动词，这样同位语从句也就转换成宾语从句(如: 上面第3个例句)

　　接下来我们看看实际考题中的句子：
　　(2002年综合A级考题阅读理解第3篇文章)
　　Effects of Environmental Pollution
　　Two spectres haunting³ conservationists have been the prospect(给“预测”这个中性词添加上了词语色彩， 变成担心， 接着把名词“担心”变成动词的“担心”))that environmental pollution might lead to the planets⁴' becoming unbearably⁵ hot or cold. One of these ghosts has now been laid, because it seems that even an increase in the amount of carbon dioxide in the atmosphere to eight times its present value will produce an increase in temperature of only 2C, which would take place over several thousand years.